<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input id="num1"/>
+
<input id="num2"/>
<input type="button" value="=" onclick="jia()"/>
<input id="num3"/><br/>

<input id="num4"/>
-
<input id="num5"/>
<input type="button" value="=" onclick="jian()" />
<input id="num6"/><br/>

<input id="num7"/>
*
<input id="num8"/>
<input type="button" value="=" onclick="cheng()"/>
<input id="num9"/><br/>

<input id="a1"/>
/
<input id="a2"/>
<input type="button" value="=" onclick="chu()" />
<input id="a3"/><br/>
</body>
<script>
    function jia() {
        num3.value=parseInt(num1.value)+parseInt(num2.value);
    }
    function jian() {
        num6.value=parseInt(num4.value)-parseInt(num5.value);
    }
    function cheng() {
        num9.value=parseInt(num7.value)*parseInt(num8.value);
    }
    function chu() {
        a3.value=parseInt(a1.value)/parseInt(a2.value);
    }
</script>
</html>